Pot type magnetic core for toroidal coil



April 18, 1967 KOUJI KAWAHARA ETAL 3,315,196

POT TYPE MAGNETIC CORE FOR TOROIDAL COIL Filed June 16, 1964 PRIOR ARAd(mm) United States Patent 3,315,196 POT TYPE MAGNETIC ICORE FORTOROIDAL CO L Kouji Kawahara, Kawasaki-shi, and Misao Takahashi, Tokyo,Japan, assignors to Fujitsu Limited, Kawasaki, Japan, a corporation ofJapan Filed June 16, 1964, Ser. No. 376,303 Claims priority, applicationJapan, June 20, 1963, 38/332,357 7 Claims. (Cl. 336- 83) The presentinvention relates to a magnetic core for a toroidal coil. -Moreparticularly, theinvention relates to a miniature magnetic core.

There is a recent tendency toward miniaturization of variouscommunicating equipment so that miniaturization of coil and transformerbecomes indispensable. There are various problems which arise in the useof a tubular shape pot-type magnetic core of conventional type. Thevalue of Q drops due to an increase of DC. resistance loss, andstability may be lost due to such increase. Furthermore, a reduction ofcoil space increases magnetic resistance and magnetic loss.Miniaturization requires high quality material and this causes anincrease in the cost of manufacture. Miniaturization has been limited bypoor magnetic concentration in the core.

The present invention concerns a magnetic core in which such problemsare entirely resolved and in which the magnetic concentration isimproved although the core is of small size. Furthermore, the core willprovide an efficient and effective coil or transformer without the useof high-quality material.

The principal object of the present invention is to provide a new andimproved miniature magnetic core.

One of the characteristics of the magnetic core of the present inventionis that it is a rectangular parallelopiped. The rectangularparallelopiped configuration of the core improves its magneticconcentration. If, however, its size ratio is not properly selected,various problems may occur in the manufacturing of the magnetic core andit becomes impossible to assure expected characteristics. Therefore, inorder to obtain good results with the rectangular parallelopipedmagnetic core, including a manufacturing process free of problems,consideration should be given to the size of each part of the magneticcore.

Another of the characteristics of the magnetic core of the presentinvention is that the size of each part is selected in accordance withpredetermined equations.

In order that the present invention may be readily carried into effect,it will now be described with reference to the accompanying drawings,wherein:

FIG. 1 is a perspective view of an embodiment of a known type ofmagnetic core;

FIG. 2 is a perspective view of an embodiment of a magnetic core of thepresent invention;

FIG. 3 is a section of the magnetic core of FIG. 2, taken along the lineIIIIII;

FIGS. 4, 5 and 6 are graphical presentations of the magnitude Wa versusH2 Patented Apr. 18, 1967 erally most effective to make the frequencyband small. When a small size magnetic core is operated in the frequencyband of 12 to 24 kilocycles, 70 to 80% of the coil loss is due to thecoil Wire loss and most of the coil wire loss is due to DC. resistanceloss. Therefore, the most suitable size of magnetic core can be obtainedfrom the condition of minimum D.C. resistance loss as follows.

The magnetic core of the present invention comprises a substantiallyrectangular parallelopiped having spaced substantially parallel top andbottom faces. A first pair of spaced substantially parallel sides issubstantially perpendicular to the top and bottom faces. A second pairof spaced substantially parallel sides is substantially per: pendicularto the top and bottom faces and to the first pair of sides. Each of thetop and bottom faces has four edges of substantially equal length Wforming a substantially square face. Each of the sides of the first pairof sides and each of the sides of the second pair of sides has top andbottom edges of substantially equal length W and side edges ofsubstantially equal length H1 forming a substantial rectangularparallelogram of each side.

The magnetic core has formed therein a substantially toroidal recess foraccommodating a substantially toroidal coil. The toroidal recess hasspaced substantially parallel top and bottom faces substantiallyparallel to the top and bottom faces of the rectangular parallelopipedand spaced a distance H2 from each other. A first substantiallycylindrical side is substantially perpendicular to the top and bottomfaces of the toroidal recess and of the rectangular parallelopiped andhas a diameter D2. A second substantially cylindrical side is coaxialwith and spaced from the first side of the toroidal recess and issubstantially perpendicular to the top and bottom faces of the toroidalrecess and of the rectangular parallelopiped and has a diameter D3. Eachof the top and bottom faces of the toroidal recess has an inner circularedge formed by the first side of the toroidal recess and an outercircular edge formed by the second side of the toroidal recess.

The magnetic core has formed therethrough an aperture of diameter D1substantially perpendicular to the top and bottom faces of said magneticcore and centrally located substantially equidistantly from the sides ofthe first and second pairs of sides thereof.

In the embodiment of FIG. 2, the magnetic core has formed in each sideof one of the first and second pairs of sides thereof a notch extendingfrom the top face to the bottom face of said magnetic core substantiallyparallel to the sides of the other of the first and second pairs ofsides thereof and to the H2 edges of the sides.

In the modification of FIG. 7, a notch similar to those Q of theembodiment of FIG. 2, is formed in each side of the magnetic core. Eachnotch has a bottom substantially juxtaposed with the second sideof thetoroidal recess at a distance Ad from each corresponding side of thefirst and second pairs of sides of the magnetic core.

In FIG. 3, the size and description of each part in millimeters is:

W is the length of the outer side of the magnetic core.

D1 is the diameter of the central aperture through the core.

D2 is the inside diameter of the toroidal recess formed in the core.

D3 is the outside diameter of the toroidal recess formed in the core.

H1 is the thickness of the magnetic core.

H2 is the thickness of the toroidal recess formed in the core.

At is the clearance between the coil and the toroidal recess formed inthe core.

The DC. resistance loss is defined by the equation:

where:

is the effective magnetic permeability.

fcu is the concentration rate of copper.

L is the inductance of the coil or winding (H).

l is the mean length of the flux path in cm.

1 is the frequency in cycles per second.

p is the specific resistance of the winding or coil in ohm-cm. A is thecross-sectional area of the core in cm.

1r(D'3+D2) is the average length of a single winding.

(D3D2) (H22At)/2 is the cross-sectional area of the toroidal recess. Ifthe average length of the winding is defined by k and thecross-sectional area of the toroidal recess is defined by Wu, the DC.resistance loss will be where p is the specific resistance of the coil.Thus, copper has a p of l.76- lohm/cm.

As is evident from this equation, the term which re lates to core sizeis only log a If W is assumed to be 14.0 mm., D1 is assumed to be 3.0mm., and At is assumed to he 0.2 mm., the calculation of Z A2 Wa isillustrated in FIGS. 4, 5 and 6, each of which illustrates Z x2 Wa toLis the ordinate in mm. In FIG. 4, H2 is the abscissa in mm., fordifferent values of 1-11. In FIG. 5, c is the abscissa in mm., fordifferent values of 1-11. In FIG. 6, a is the abscissa in mm., fordifferent values of H1. These curves enable the determination of thevalue of H2 which provides the minimum value of 1 A2 wL with respect toH1. This results in the selection of H1 and H2 values for minimum D.C.resistance loss.

If a, 0, H1 and H2 are selected as follows, a good result is obtained:

Hl=11 to 14 mm. H2=8 to 10 mm. a=4.8 to 5.2 mm. c=14 to 15 mm.

A desirable size in practical use is obtained if W is 14 mm. However, inactuality manufacturing problems should be taken into consideration. Ina rectangular parallelopiped type magnetic core of the presentinvention, Ad shown in FIG. 7, presumably creates a manufacturingproblem.

The cross section of the outside ring portion is not uniform, as opposedto conventional magnetic cores. Thus, during the manufacture of amagnetic core, a part may break or crack and may thus affect theelectrical characteristics of the core. Accordingly, it is desirablethat the value of Ad be as large as possible. It is, however,undesirable :to make the value of Ad too large, since too large a valueof Ad causes a drop in the magnitude of the quality factor Q.

The relation between Ad and Q is shown in FIG. 7, and from the curve ofFIG. 7, the value Ad=.8 mm. can be selected. The size of the magneticcore is obtained from the aforementioned results. In general, the sizeof the stantially perpendicular to the top and bottom faces of saidtoroidal recess and of said rectangular parallelopiped and having adiameter D3 mm., each of the top and bottom faces of said toroidalrecess having an inner magnetic core follows similarly to theaforedescribed circular edge formed by the first side of said toroidalcalculations. Therefore, if the aforedescribed size ratio recess and anouter circular edge formed by the second is applied to another core ofdifferent size, the various side of said toroidal recess, the ratio W/D3ranging in size ratios for the magnetic core may be immediately obvaluefrom 1.00 to 1.15, the ratio W/D2 ranging in value tained. Thesepreferred size ratios are: from 1.50 to 2.40. the ratio W/Hl ranging invalue from- W/D3:1.00 to L15 0.90 to 1.60 and the ratio Hl/HZ ranging invalue from 1.20 to 1.50. W/D2=1.50 to 2.40

2. A magnetic core as claimed in claim 1, wherein W/Hl 0.90 to 1.60

said magnetic core has formed therethrough an aperture H1/H2 -1.20 to1.50

Ad 4 to 0 8 mm substantially perpendicular to said top and bottom facesthereof and centrally located substantially equidistantly The magneticcore of the present invention for a from the sides of said first andsecond pairs of sides toroidal coil may 'be used in a wide range, suchas for a thereof. filter, or loading coil, etc. The following is anexample A magnetic core as claimed in claim 1, wherein in wh1ch the coreis used w1th a band pass filter element said magnetic core has formed ineach side of one of the and ton hhe loadlhg c011 and 15 of Small Wlthhttle first and second pairs of sides thereof a notch extending loss.The transformer D-.C. resistance loss Rdc/wL is refrom the top f to thebottom f of said magnetic dhced about Over that of a cohvehhohal maghehccore substantially parallel .to the sides of the other of core f SameThe maghgh? P of the Present said first and second pairs of sidesthereof.

invention has a wide range of utilization and applica- A magnetic coreas claimed in claim 1 wherein tloh- I 25 said magnetic core has formedin each side of each of the In an apphcatlon Wlth a band P21SSfilterfirst and second pairs of sides thereof a notch extending from thetop face to the bottom face of said magnetic Slze fi g g z core m coresubstantially parallel to the sides of the other of said first andsecond pairs of sides thereof. 1]. X X o 5. A magnetic core as claimedin claim 4, wherein Q 3 it mh each notch has a bottom substantiallyiuxtaposed with 270 e the second side of said toroidal recess. 320 6. Amagnetic core as claimed in claim 1, wherein said 340 r magnetic corehas formed therethrough an aperture substantially perpendicular to saidtop and bottom faces where is the diameter in mm. of the magnetic coreand thereof and centrally located substantially equidistantly 14 x 8.4is a magnetic core having a diameter of 14 mm. from the sides of saidfirst and second pairs of sides thereand an altitude of 8.4 mm. of andwherein said magnetic core has formed in each In an application as achannel filter: side of one of the first and second pairs of sidesthereof Item Size of magnetic core Note 30x19 21x21x21 Inductivlty100mh./37mh 100mh./37ml1.-

(Side Cot.) (Phantom Cct.). Effectiveresistanee, 1,800 c.ls 16.60 15.80Side.

Do. .20 7.70 Phantom. Hysteresis factor, AR 800 c./s 0150/1119. 0.120/maSide.

Do 0.0359/ma 0.03S2/ma Phantom. Magnetic stability" 0.90%- 0.17%-

We claim: a notch extending from the top face to the bottom face 1. Amagnetic core for a substantially toroidal coil, of said magnetic coresubstantially parallel to the sides comprising a substantiallyrectangular parallelopiped hav of the other of said first and secondpairs of sides thereof. ing spaced substantially parallel top and bottomfaces, 7. A magnetic core as claimed in claim 1, wherein a first pair ofspaced substantially parallel sides substansaid magnetic core has formedtherethrough an aperture tially perpendicular to said top and bottomfaces and a substantially perpendicular to said top and bottom facessecond pair of spaced substantially parallel sides substanthereof andcentrally located substantially equidistantly tially perpendicular tosaid top and bottom faces and to from the sides of said first and secondpairs of sides said first pair of sides, each of said top and bottomfaces thereof and wherein said magnetic core has formed in having fouredges of substantially equal length W mm., each side of each of thefirst and second pairs of sides each of the sides of said first pair ofsides and each of thereof a notch extending from the top face to thebotthe sides of said second pair of sides having top and tom face ofsaid magnetic core substantially parallel to bottom edges ofsubstantially equal length W mm. and the sides of the other of saidfirst and second pairs of side edges of substantially equal length H1mm., said sides thereof.

magnetic core having formed therein a substantially toroidal recess fora substantially toroidal coil, said References Clted y the Examinertoroidal recess having substantially parallel top and bot- UNITED STATESPAT N S tom faces substantially parallel to the top and bottom 3,068,43612/1962 Holmberg et aL X faces of said rectangular parallelepiped andspaced a distance H2 mm. from each other, a first substantially OTHERREFERENCES cylindrical side substantially perpendicular to the top andbottom faces of said toroidal recess and of said rectangularparallelopiped and having a diameter D2 mm. and a second substantiallycylindrical side coaxial with and spaced from the first side of saidtoroidal recess and sub- Brackmann: German appl. No. 1,555,492, 1963.

LEWIS H. MYERS, Primary Examiner. L. EASKIN, T. J. KO'ZMA, AssistantExaminers.

pub. Oct. 10,

1. A MAGNETIC CORE FOR A SUBSTANTIALLY TOROIDAL COIL, COMPRISING ASUBSTANTIALLY RECTANGULAR PARALLELOPIPED HAVING SPACED SUBSTANTIALLYPARALLEL TOP AND BOTTOM FACES, A FIRST PAIR OF SPACED SUBSTANTIALLYPARALLEL SIDES SUBSTANTIALLY PERPENDICULAR TO SAID TOP AND BOTTOM FACESAND A SECOND PAIR OF SPACED SUBSTANTIALLY PARALLEL SIDES SUBSTANTIALLYPERPENDICULAR TO SAID TOP AND BOTTOM FACES AND TO SAID FIRST PAIR OFSIDES, EACH OF SAID TOP AND BOTTOM FACES HAVING FOUR EDGES OFSUBSTANTIALLY EQUAL LENGTH W MM., EACH OF THE SIDES OF SAID FIRST PAIDOF SIDES AND EACH OF THE SIDES OF SAID SECOND PAIR OF SIDES HAVING TOPAND BOTTOM EDGES OF SUBSTANTIALLY EQUAL LENGTH W MM. AND SIDE EDGES OFSUBSTANTIALLY EQUAL LENGTH H1 MM., SAID MAGNETIC CORE HAVING FORMEDTHEREIN A SUBSTANTIALLY TOROIDAL RECESS FOR A SUBSTANTIALLY TOROIDALCOIL, SAID TOROIDAL RECESS HAVING SUBSTANTIALLY PARALLEL TOP AND BOTTOMFACES SUBSTANTIALLY PARALLEL TO THE TOP AND BOTTOM FACES OF SAIDRECTANGULAR PARALLELOPIPED AND SPACED A DISTANCE H2 MM. FROM EACH OTHER,A FIRST SUBSTANTIALLY CYLINDRICAL SIDE SUBSTANTIALLY PERPENDICULAR TOTHE TOP AND BOTTOM FACES OF SAID TOROIDAL RECESS AND OF SAID RECTANGULARPARALLELOPIPED AND HAVING A DIAMETER D2 MM. AND A SECOND SUBSTANTIALLYCYLINDRICAL SIDE COAXIAL WITH AND SPACED FROM THE FIRST SIDE OF SAIDTOROIDAL RECESS AND SUB-